[rtl] IP useage from rtlinux, reply to Richard Teltz

["Warren Postma" <embed@geocities.com>]

Richard Teltz asked:

>Has anyone ported IP support to the rtlinux kernel level?
>Does anyone have any insight or suggestions as to how I might
>approach my problem?  Any suggestions would be appreciated.

This is my first posting to this mailing list. I am relatively new to
RT-Linux, but your message interests me since we're considering moving a
non-realtime embedded DOS application (Diesel GenSet control) towards some
new applications that have realtime reliability requirements although not so
much realtime performance requirements, so here goes...


On one hand if you're using Ethernet, performance is non-deterministic, and
even less deterministic over a WAN or the Internet, running the protocol  in
a high priority RT task would not guarantee  deterministic performance.  You
say you are using UDP, which means that delivery is not guaranteed,
especially on a WAN, meaning that retries must be acceptable. So in that
case, what do you hope to gain by porting IP support to the rtlinux kernel
level?  You can still communicate between RTLINUX processes between machines
by using QUEUES to communicate to a Broker of your own design that then does
communications through the network.

On the other hand, if you did have hard realtime network requirements and
need deterministic performance you could use an ARCNET based system, and
then I could see you might want network support inside the RT kernel level.
This is something that QNX excels at with it's "transparent" (albeit
proprietary) network message passing. I am curious also if anyone has tried
to do a QNX-like RTOS Network Message Passing system via ArcNet or TokenRing
(or any other deterministic bus or network technology) using RT-Linux.  I
would think that TCP/IP would not have to be used, and a simpler and more
performance oriented RT specific protocol could be developed. This is done
in many cases in industrial controls equipment, such as the Opto 22 Mistic
controller network and is one of QNX's strongest selling points for
networked RTOS devices.

Warren Postma





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